The present invention relates to a new and improved construction of an electro-optical apparatus for the detection of the presence of liquids, which is of the type comprising at least one monochromatic infrared transmitter which is arranged at the region of a hollow body probe composed of a synthetic high molecular substance or material and totally reflecting the infrared radiation, as well as there being provided at least one infrared receiver and a circuit for signal processing.
Such equipment is designated in the art as liquid sensors. In Swiss Pat. No. 512,060 there is taught to the art a compact structural unit which has a high response sensitivity and is extensively non-sensitive to mechanical loads and does not require any subsequent adjustments.
The light-conducting body, used with the prior art equipment, for the detection of the presence of liquid must have high optical transparency, and therefore, in practice is fabricated from acrylic glass.
Owing to the limited resistance of acrylic glass as well as similar light-conducting products with respect to liquids which can be considered to be aggressive, the use of such type liquid sensors is limited as is also their longevity.
All of the heretofore known liquid sensors or feelers additionally require a relatively high transmitting energy of the light-emitting diode, in order to insure for a reproducible response behavior. It is known that for this reason the employment of such type devices, especially the use thereof in conjunction with highly explosive media, is forbidden for reasons of safety in a number of countries.